The surface structure of CeO2(001) single crystals studied by elevated temperature STM

We have studied the atomic structure of the CeO2(001) surface as an example for a polar "type III" surface by scanning tunnelling microscope (STM), lo w energy electron diffraction (LEED) and atomistic simulation. High resolut ion STM on single crystalline CeO2(001) revealed a root2/2(3 x 2)R45 degree s surface reconstruction. Calculation confirmed oxygen in the top layer. Up on removal of further oxygen, Ce ions in the subsurface layer are reduced t o Ce3+. Because oxygen from bridging positions is removed during this proce ss the surface maintains its root2/2(3 x 2)R45 degrees reconstruction. Atom istic modelling showed that an arrangement of Ce3+ ions in lines is energet ically favourable compared to other structures. Among a number of surfaces considered the root2/2(3 x 2)R45 degrees reconstruction was energetically m ost favoured. These results confirm the experimental findings and show that polar "type III" surfaces in metal oxides reduce their surface energy by r econstruction. After reoxidation and annealing a c(3 x 3) surface reconstruction was found , LEED investigations confirmed the STM results and indicate some disorder of the surface in the [110] direction. (C) 2001 Elsevier Science B.V. All r ights reserved.